Conventionally, a sensitive element is manufactured by using sensing bodies having electrical characteristics of dielectric constant changed by a physical or chemical interaction between the sensing bodies and an external factor such as humidity, etc. to be detected.
FIG. 1 shows a first conventional example of such a sensitive element. In this sensitive element, a lower electrode 32, a sensitive thin film 33 composed of a humidity sensing high polymer, and an upper electrode 34 are sequentially stacked on an insulating substrate 31 such as glass, constituting a sensitive portion 35 composed of a capacitor with the sensitive thin film 33 as a dielectric. The external factor such as humidity to be detected is absorbed to the sensitive thin film 33 through the upper electrode 34, and is discharged through the upper electrode 34 so that the upper electrode 34 is formed by a very thin metallic evaporation thin film having a thickness of several hundred angstroms to provide conductivity and permeability of moisture, etc. Further, one end side of the upper electrode 34 extends downwards onto the upper face of the insulating substrate 31 in a stepped portion at an end edge of the sensitive thin film 33, forming a connecting pad 34a for connecting the upper electrode 34 to a detecting circuit. Reference numeral 32a is a connecting pad on the side of the lower electrode 32.
The external factor such as humidity, etc. to be detected is absorbed to the sensitive thin film 33, and the change in dielectric constant, i.e., the change in capacitance between the upper electrode 34 and the lower electrode 32 is outputted to detect the humidity as a change in electrical signal by the detecting circuit.
However, in the above first conventional example, since the upper electrode 34 is formed by the metallic evaporation after the formation of the sensitive thin film 33 composed of a humidity sensing high polymer, the sensitive thin film 33 is heated in the evaporation and a thermal reaction or other reaction is caused between the sensitive thin film 33 and the metal for the upper electrode 34 stacked by the evaporation, causing deterioration on a surface of the sensitive thin film 33. Also, since the upper electrode 34 is formed by a very thin metallic evaporation thin film having a thickness of several hundred angstroms, dispersion is caused with respect to permeability of moisture and conductivity, so that the electrical characteristics of the elements tend to be dispersed. Further, since the upper electrode 34 is formed by the very thin metallic evaporation as mentioned above, the thin film tends to be broken in the stepped portion at the end edge of the sensitive thin film 33 in the evaporation, thereby lowering the yield in manufacture and reducing the reliability.
FIG. 2 shows a second conventional example of the sensitive element. In this conventional example, two lower electrodes 37 and 38 are disposed on an insulating substrate 31 at a suitable distance, and a sensitive thin film 39 and an upper electrode 40 are sequentially stacked on the two lower electrodes 37 and 38. One capacitor is formed by the one lower electrode 37 and the upper electrode 40 with the sensitive thin film 39 as a dielectric, and another capacitor is formed by the other lower electrode 38 and the upper electrode 40, so that a sensitive portion 41 is constructed by the two capacitors connected in series to each other.
Even in the second conventional example, similar to the first conventional example, the external factor such as humidity, etc. to be detected is absorbed or discharged with respect to the sensitive thin film 39 through the upper electrode 40 Therefore, the upper electrode 40 is formed by a very thin metallic evaporation thin film having a thickness of several hundred angstroms. Accordingly, even in the second conventional example, a thermal reaction or other reaction is caused between the sensitive thin film 39 and the metal in the evaporation of the metal for the upper electrode 40 so that a surface of the sensitive thin film 39 might be deteriorated, and dispersion is caused with respect to the permeability of moisture and conductivity so that the electrical characteristics of the elements tend to be dispersed.
As mentioned above, in the first conventional example, the upper electrode is formed by the metallic evaporation after the formation of the sensitive thin film, a thermal reaction or other reaction is caused between the sensitive thin film and the metal in the evaporation, so that a surface of the sensitive thin film might be deteriorated. Also, since the upper electrode is formed by a very thin film having a thickness of several hundred angstroms, dispersion is caused with respect to the permeability of moisture and conductivity, and the electrical characteristics of the elements tend to be dispersed. Further, the upper electrode tends to be broken in a stepped portion at an end edge of the sensitive thin film in the evaporation, thereby reducing the yield in manufacture and reliability.
In the second conventional example, since the upper electrode is formed by a very thin metallic evaporation thin film having a thickness of several hundred angstroms, similarly to the first conventional example, a surface of the sensitive thin film might be deteriorated at the manufacturing time thereof, and dispersion is caused with respect to the permeability of moisture and conductivity and the electrical characteristics of the elements tend to be dispersed.
Further, in another sensitive element, the electrical characteristics of the sensitive element are deteriorated by hysteresis characteristics and the speed in response is low, and a humidity sensitive material having a thermally low resistance cannot be used to avoid the deterioration of the sensitive thin film. Further, in the conventional manufacturing processes of the humidity sensitive element, it is necessary to perform a process for forming the upper electrode and a patterning process of the humidity sensitive thin film, thereby simplifying the processes.